Trench cutting apparatus and method

ABSTRACT

A trench cutting apparatus comprises a main body portion, ground contacting conveying means on which the body portion is mounted and by which the apparatus can traverse the ground and at least one soil cutting device operable to cut a trench wherein the attitude of the soil cutting device is adjustable between a first use configuration configured for cutting a linear trench portion and a second use position configured for cutting a curved trench portion, said second use position being selected to minimise undercutting of a trench wall as said curved trench portion is formed.

This invention relates to an apparatus and method for cutting a trenchin the ground and more especially (but not exclusively) for cutting atrench in the bed of a body of water such as the bed of a lake or thesea bed. The invention relates in particular to apparatus and a methodwhich avoids or reduces undercutting of the trench when executing a turnof the trench.

BACKGROUND

The formation of trenches in the ground is a well known requirement andis typically needed for burying utility supply means such as gas andwater pipes and electricity and telecommunications cables. In underwaterenvironments, the cutting of a trench is typically required for burialof pipes and cables and requires specially constructed or adaptedequipment configured for underwater conditions, such as the nature ofthe seabed. Herein “seabed” is used to refer to the bed of the sea or ofa lake or even a river, unless the context requires otherwise.

Various apparatus for constructing a trench are known in the art. Thesecan include soil cutting devices in the form of ploughs, jettingapparatus (for underwater use) and chain cutters which form the desiredtrench. Typically the soil cutting device is mounted on a vehicle whichmoves over the ground (e.g. the seabed) either under its own power of byexternal means. For example, the trench cutting vehicle might be towedby a tractor vehicle or by a ship at the surface. Generally it ispreferred that the trench cutting vehicle is self-powered. Typically thetrench cutting vehicle is mounted on endless articulated tracks.

An issue encountered by trench forming vehicles of this type is when thecourse of the trench executes a turn, in particular a turn of smallturning radius. In this situation, it is possible for the soil cuttingdevice (more especially where the soil cutting device is a chain cutteror jetting device) to undercut the trench wall on the outer side of thecurved portion of the trench. This has the effect of de-stabilising thetrench wall. Also, it is possible for the soil cutting device such as achain cutter to become wedged or jammed with respect to the trench wall

BRIEF SUMMARY OF THE DISCLOSURE

The present invention seeks to ameliorate or overcome the above problem.In particular, the present invention seeks to provide trench cuttingapparatus and a method of trench cutting which reduces, minimises oravoids the undercutting of the trench wall as a turn in the trench isexecuted. The wall of the trench is formed at a desired angle, mostpreferably substantially vertical.

In accordance with the a first aspect of the present invention there isprovided a trench cutting apparatus comprising a main body portion,ground contacting conveying means on which the body portion is mountedand by which the apparatus can traverse the ground and at least one soilcutting device operable to cut a trench wherein the attitude of the soilcutting device is adjustable between a first use configurationconfigured for cutting a linear trench portion and a second use positionconfigured for cutting a curved trench portion, said second use positionbeing selected to minimise undercutting of a trench wall as said curvedtrench portion is formed.

In preferred embodiments the soil cutting device is a chain cutter or ajetting cutter.

In preferred embodiments the apparatus further comprises a controldevice wherein the attitude of the soil cutting device is adjustableunder the control of the control device.

In some preferred embodiments the attitude of the soil cutting device isautomatically adjusted by the control device in dependence on the radiusof curvature required for the trench being formed.

In some preferred embodiments the soil cutting device is a chain cuttercomprising a plurality of soil cutting teeth mounted for movement in anendless loop, the chain cutter having, in an operational position, alower end at which the soil cutting teeth cut the soil to form thetrench and a upper end at which the teeth are spaced apart from thesoil, said lower end having an outer edge and an inner edge whichrespectively define opposed boundaries of the trench being cut, andwherein the adjustment in the attitude of the chain cutter is such thatat least a portion of said outer edge is displaced towards the directionof curvature of the trench.

Preferably in these embodiments the attitude of the chain cutter isadjusted by rotating the chain cutter about a nominally horizontal axis.Said horizontal axis is preferably at least approximately parallel tothe direction of motion of the trench cutting axis at any given time.

In other preferred embodiments the soil cutting device is a jettingcutter having, in an operational position, a first portion from whichcutting fluid is expelled along a line of action to cut the soil to formthe trench and a second portion which is in fluid communication with asupply of cutting fluid and wherein the adjustment in the attitude ofthe jetting cutter is such that said line of action of the cutting fluidis displaced towards the direction of curvature of the trench.

Preferably in these other preferred embodiments the attitude of thejetting cutter is adjusted by rotating the jetting cutter about anominally horizontal axis. Said horizontal axis is preferably at leastapproximately parallel to the direction of motion of the trench cuttingaxis at any given time.

In preferred embodiments the apparatus further comprises actuatorscoupled to the soil cutting device and configured to adjust the attitudeof the soil cutting device by rotating the soil cutting device aboutsaid horizontal axis.

Preferably the change in attitude of the soil cutting device is effectedby a change in attitude of the body portion, the attitude of the soilcutting device being maintained in fixed relation to the body portion.

Preferably the attitude of the body portion is adjustable by adjustmentof the spacing of one or both of the ground contacting conveying meanswith respect to the body portion.

According to a second aspect of the present invention there is provideda method of cutting a trench comprising providing a trench cuttingapparatus having an soil cutting device which is adjustable betweenfirst and second attitudes and prior to cutting a curved portion of thetrench, adjusting the attitude of the soil cutting device to an attitudein which undercutting of the trench wall of said curved portion isminimised.

In preferred embodiments of the second aspect of the invention theattitude of the soil cutting device is adjusted in dependence on theradius of curvature of the trench being formed

Preferably the adjustment in the attitude of the soil cutting devicecomprises rotating the soil cutting device about a nominally horizontalaxis. Said horizontal axis is preferably at least approximately parallelto the direction of motion of the trench cutting axis at any given time.

Preferably the trench cutting apparatus comprises a main body portion towhich the soil cutting device is attached and the adjustment in theattitude of the soil cutting device comprises adjusting the attitude ofthe main body portion.

In particularly preferred embodiments the trench cutting apparatus is anapparatus as defined in the first aspect of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention are further described hereinafter, by wayof example only, with reference to the accompanying drawings, in which:

FIG. 1 is a representation of a typical trench cutting apparatus;

FIG. 2 a shows schematically a plan view of a trench and a cutting partof a trench cutting apparatus according to the prior art indicating thepotential for undercutting of the trench wall;

FIG. 2 b is similar to FIG. 2 a and illustrates the reduction in theundercutting of the trench wall achieved by the apparatus and method ofthe invention;

FIG. 3 a is a view of the outline of a trench cutting device viewed fromthe front and illustrating the degree of undercutting of the trench wallwhich can occur with trench cutting arrangements of the prior art;

FIG. 3 b is similar to FIG. 3 a and shows the outline of a trenchcutting device when the attitude thereof is adjusted according to thepresent invention and illustrating the reduction in the degree ofundercutting which is achieved;

FIG. 4 a is a plan view of a typical trench cutting device according tothe present invention;

FIG. 4 b is a side view of the trench cutting device of FIG. 4 a; and

FIG. 4 c is a perspective view of the trench cutting device of FIGS. 4 aand 4 b.

DETAILED DESCRIPTION

Referring now to the drawings, the present invention addresses theproblem of the formation of undercuts in a trench side wall in curvedportions of a trench when the trench is formed using apparatus of theprior art. Undercuts are formed with prior art apparatus in the outertrench wall, that is, the wall in a curved section of trench having agreater radius of curvature than an opposed inner trench wall.

FIG. 1 shows on example of a prior art trenching apparatus 100, in thisparticular case configured for forming a trench 102 in the seabed 104and simultaneously burying a pipeline 106 in the trench 102. For theavoidance of doubt, the apparatus according to the present invention mayusefully be equipped with means both for trench forming and forsimultaneous burying of a pipeline, but pipe burying means are not perse an essential feature of the apparatus of the invention. The prior artapparatus 100 includes a main body 108 and ground contacting conveyingmeans 110 in the form of endless articulated tracks on which the mainbody 108 is mounted and by means of which the apparatus 100 moves overthe seabed 104 in the direction of arrow A. The prior art trenchingapparatus 100 as illustrated in FIG. 1 includes primary and secondarysoil cutting devices 112, 114, it being noted for the avoidance of doubtthat there is no requirement for the apparatus according to the presentinvention to include both primary and secondary soil cutting devices,although useful embodiments may do so. In FIG. 1, the primary soilcutting device 112 is a chain cutter and the secondary soil cuttingdevice 114 is a jetting cutter. The chain cutter 112 comprises anendless belt 116 carrying a plurality of soil cutting teeth 118. Thebelt 116 is driven by suitable drive means so that the soil cuttingteeth move in an endless loop during the course of which the teeth 118contact, and displace, soil so to form the trench 102. The chain cutter112 is mounted to pivot about horizontal axis 120 in order to adjust thedepth of cut of the trench. Horizontal axis 120 passes transversely withrespect to the body 108, that is, perpendicular with respect to thedirection of travel A of the apparatus 100. Jetting cutter 114 comprisesa plurality of outlets or nozzles from which fluid (typically water) isexpelled under high pressure to displace soil.

FIGS. 2 a and 3 a and FIGS. 2 b and 3 b respectively illustrate theformation of an undercut using prior art apparatus and the avoidance ofundercut formation using the apparatus of the invention. In FIGS. 2 aand 2 b the trench is illustrated schematically at 202A and 202Brespectively. The centre lines of the trenches are shown at 240A and240B. In the right hand portions of FIGS. 2A and 2B, the trenches 202Aand 202B are substantially linear and the problem of undercutting of thetrench walls does not arise. Thus, the orientation of the trench wallsis about vertical, generally in alignment with the side edges of thesoil cutting devices 200A and 200B. If in any particular case the soilcutting device is set an angle to the vertical (e.g. when cutting aV-shaped trench) then the trench walls follow the orientation of thesoil cutting device.

At about points 230A and 230B respectively the trenches 202A and 202Bbegin to curve or turn, in the illustrated case to the left. In FIG. 2 athe illustrated positions of soil cutting devices 200A and 200AA in theleft portion of the Figure indicate the degree of undercutting of thetrench wall which can occur, it being noted that portions of the soilcutting devices 200A 200AA extend beyond the indicated boundaries of thetrench. In FIG. 2 a (and in FIG. 3 a) according to the prior art method,the soil cutting device 200 a, 200AA is maintained in a verticalorientation. In contrast, in FIG. 2B which illustrates an adjustment ofthe attitude of the trench cutting device 200B, 200BB according to theinvention, the undercuts are avoided, as can be noted at 232B and 234B,and substantially vertical trench walls are achieved.

The same effect is illustrated in FIGS. 3 a and 3 b. In FIG. 3 a, thesoil cutting device 200A (shown schematically) produces an undercut 232Awhen executing a turn (because of the essentially vertical orientationof the soil cutting device 200A) whereas in FIG. 3 b, the soil cuttingdevice 200B according to the invention produces no such undercut, as canbe noted at 232B.

FIGS. 4 a to 4 c show a typical arrangement of a trench cuttingapparatus 400 according to the invention, the apparatus 400 including amain body portion 408 (shown schematically) on which is mounted a soilcutting device 412. The main body portion 408 is mounted on groundcontacting conveying means (not illustrated) of any suitable type suchas endless tracks of the kind illustrated at 110 in FIG. 1.

The soil cutting device as illustrated in FIGS. 4 a to 4 c is a chaincutter device which includes a plurality of teeth (not specificallyillustrated) mounted to process around an endless path in the samemanner as discussed in relation to chain cutter 112 in FIG. 1. The chaincutter 412 is mounted to the main body 408 at a pivot 420. Theinclination of the chain cutter 412 is controlled by means of anactuator 452, such as a hydraulic actuator, mounted on an arm 450 bymeans of which the orientation of the chain cutter 412 about the pivot420 can be adjusted in order to determine the depth of the trench beingcut.

As noted above, in accordance with the present invention, the attitudeof the soil cutting device is adjustable in order to minimise or preventthe formation of undercuts in the walls of the trench being formed incases where the trench is other than linear. The problem of formingundercuts in the trench walls is particularly acute with prior artapparatus when it is necessary to form curves or turns in the trench ofsmall radius. In its broadest sense, the attitude of the soil cuttingdevice 412 is changed by adjusting the lower end 412 a of the soilcutting device by displacement of at least a part or portion thereof inthe direction of curvature of the trench. That is, if the trench curvesto the left (with respect to the direction of trench cutting), then thelower end portion 412 a of the soil cutting device 412 is also adjustedto the left and, likewise if the trench curves to the right (withrespect to the direction of trench cutting), then the lower end portion412 a of the soil cutting device 412 is also adjusted to the right.

In preferred embodiments, for the adjustment of the attitude of the soilcutting device 412, the soil cutting device 412 is rotated about ahorizontal axis such as axis 454 illustrated in FIGS. 4 b and 4 c, suchthat a lower part 412 a of the trench cutting device 412 is moved awayfrom the outer trench wall. Axis 454 preferably is substantiallyparallel to the direction of travel of the apparatus 400 and willgenerally pass through the soil cutting device 412. Rotation of the soilcutting device 412 about axis 454 is indicated by arrows 454 t (noparticular significance being given to the direction of the arrows inthe Figures). In preferred operational orientations of the soil cuttingdevice 412, where a turn is to be made to the right, the soil cuttingdevice 412 is rotated about axis 454 in an anti-clockwise(counter-clockwise) sense and, similarly where a turn is to be made tothe left, the soil cutting device 412 is rotated about axis 454 in aclockwise sense.

The apparatus 400 according to the invention is provided with suitableactuating means for adjusting the attitude of the soil cutting device412, these actuating means being shown generally at 456 in FIG. 4 a.Suitable actuating means include hydraulic actuators.

The apparatus 400 according to the invention most preferably furtherincludes a control device, such as an electronic controller, whichcontrols the adjustment of the attitude of the soil cutting device 412(via actuators 456). Such control device may rely on the manual inputsof an operator, but in more preferred arrangements the control devicedetermines the required attitude of the soil cutting devices 412 atleast partially automatically. For example, the control device maydetermine the attitude of the soil cutting device 412 on the basis ofpositional data relating to the steering system of the apparatus 400and/or reference data relating to the required curvature of the trench.

In a further alternative construction, the attitude of the soil cuttingdevice 412 may be adjusted by adjusting the attitude of the main body408 of the apparatus on which the soil cutting device 412 is mounted.This may be achieved by providing adjustment of the height of the groundcontacting conveying means (e.g. endless articulated tracks) withrespect to the body portion. In other words, the distance of therespective conveying means, primarily in the vertical plane, is adjustedso that the conveying means at one side of the main body 408 is at agreater displacement from the main body 408 than the conveying means atthe opposite side of the body. The body 408 must thus adopt an inclinedattitude with respect to the horizontal and the soil cutting device 412is correspondingly inclined. In practical terms, for cutting of a trenchwhich curves to the left, the right hand side of the main body is maderelatively higher and the left hand side is made relatively lower, andvice versa for cutting a trench which curves to the right.

The details of the present invention have been described primarilyherein in relation to the use of a chain cutter as the soil cuttingdevice. It is noted that the principles of the invention are applicablealso to the use of jetting tools (jetting cutters) as the soil cuttingdevice. Jetting cutters expel one or more jets of high pressure cuttingfluid—normally water)—in order to displace soil and form the trench. Theline of action of the jets of cutting fluid (i.e. the direction in whichthe cutting fluid is expelled) is determined by the orientation of theone or more nozzles from which the cutting fluid is expelled. Typicallythe (or each) nozzle is mounted at an end of an arm. The presentinvention contemplates the adjustment of the attitude of such an arm inorder to adjust the line of action of the (or each) jet of cuttingfluid, the line of action being adjusted at least generally in thedirection in which the trench is to turn or curve.

Throughout the description and claims of this specification, the words“comprise” and “contain” and variations of them mean “including but notlimited to”, and they are not intended to (and do not) exclude othermoieties, additives, components, integers or steps.

Throughout the description and claims of this specification, thesingular encompasses the plural unless the context otherwise requires.In particular, where the indefinite article is used, the specificationis to be understood as contemplating plurality as well as singularity,unless the context requires otherwise.

Features, integers, characteristics, compounds, chemical moieties orgroups described in conjunction with a particular aspect, embodiment orexample of the invention are to be understood to be applicable to anyother aspect, embodiment or example described herein unless incompatibletherewith. All of the features disclosed in this specification(including any accompanying claims, abstract and drawings), and/or allof the steps of any method or process so disclosed, may be combined inany combination, except combinations where at least some of suchfeatures and/or steps are mutually exclusive. The invention is notrestricted to the details of any foregoing embodiments. The inventionextends to any novel one, or any novel combination, of the featuresdisclosed in this specification (including any accompanying claims,abstract and drawings), or to any novel one, or any novel combination,of the steps of any method or process so disclosed.

The reader's attention is directed to all papers and documents which arefiled concurrently with or previous to this specification in connectionwith this application and which are open to public inspection with thisspecification, and the contents of all such papers and documents areincorporated herein by reference.

1. A trench cutting apparatus comprising a main body portion, groundcontacting conveying means on which the body portion is mounted and bywhich the apparatus can traverse the ground and at least one soilcutting device operable to cut a trench wherein the attitude of the soilcutting device is adjustable between a first use configurationconfigured for cutting a linear trench portion and a second use positionconfigured for cutting a curved trench portion, said second use positionbeing selected to minimise undercutting of a trench wall as said curvedtrench portion is formed.
 2. Apparatus as claimed in claim 1 wherein thesoil cutting device is a chain cutter or a jetting cutter. 3 Apparatusas claimed in claim 2 further comprising a control device wherein theattitude of the soil cutting device is adjustable under the control ofthe control device.
 4. Apparatus as claimed in claim 3 wherein theattitude of the soil cutting device is automatically adjusted by thecontrol device in dependence on the radius of curvature required for thetrench being formed.
 5. Apparatus as claimed in claim 2 wherein the soilcutting device is a chain cutter comprising a plurality of soil cuttingteeth mounted for movement in an endless loop, the chain cutter having,in an operational position, a lower end at which the soil cutting teethcut the soil to form the trench and a upper end at which the teeth arespaced apart from the soil, said lower end having an outer edge and aninner edge which respectively define opposed boundaries of the trenchbeing cut, and wherein the adjustment in the attitude of the chaincutter is such that at least a portion of said outer edge is displacedtowards the direction of curvature of the trench.
 6. Apparatus asclaimed in claim 5 wherein the attitude of the chain cutter is adjustedby rotating the chain cutter about a nominally horizontal axis. 7.Apparatus as claimed in claim 2 wherein the soil cutting device is ajetting cutter having, in an operational position, a first portion fromwhich cutting fluid is expelled along a line of action to cut the soilto form the trench and a second portion which is in fluid communicationwith a supply of cutting fluid and wherein the adjustment in theattitude of the jetting cutter is such that said line of action of thecutting fluid is displaced towards the direction of curvature of thetrench.
 8. Apparatus as claimed in claim 7 wherein the attitude of thejetting cutter is adjusted by rotating the jetting cutter about anominally horizontal axis.
 9. Apparatus as claimed in claim 6 furthercomprising actuators coupled to the soil cutting device and configuredto adjust the attitude of the soil cutting device by rotating the soilcutting device about said horizontal axis.
 10. Apparatus as claimed inclaim 5 wherein the change in attitude of the soil cutting device iseffected by a change in attitude of the body portion, the attitude ofthe soil cutting device being maintained in fixed relation to the bodyportion.
 11. Apparatus as claimed in claim 10 wherein the attitude ofthe body portion is adjustable by adjustment of the spacing of one orboth of the ground contacting conveying means with respect to the bodyportion.
 12. A method of cutting a trench comprising providing a trenchcutting apparatus having an soil cutting device which is adjustablebetween first and second attitudes and prior to cutting a curved portionof the trench, adjusting the attitude of the soil cutting device to anattitude in which undercutting of the trench wall of said curved portionis minimised.
 13. A method as claimed in claim 12 wherein the attitudeof the soil cutting device is adjusted in dependence on the radius ofcurvature of the trench being formed
 14. A method as claimed in claim 12wherein the adjustment in the attitude of the soil cutting devicecomprises rotating the soil cutting device about a nominally horizontalaxis.
 15. A method as claimed in claim 12 wherein the trench cuttingapparatus comprises a main body portion to which the soil cutting deviceis attached and the adjustment in the attitude of the soil cuttingdevice comprises adjusting the attitude of the main body portion.
 16. Amethod as claimed in claim 12 wherein the trench cutting apparatus is anapparatus as claimed in claim 1.